# CVE-2026-72916

## Summary

- **CVE ID:** CVE-2026-72916
- **Severity:** MEDIUM
- **CVSS Score:** 6.3 (CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:L)
- **CWE:** CWE-918, CWE-1286
- **Published:** Aug 10, 2026
- **Last Modified:** Aug 13, 2026

## Description

Mastodon is a free, open-source social network server based on ActivityPub. Prior to 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1, PrivateAddressCheck.private_address? in app/lib/private_address_check.rb normalized IPv4-mapped IPv6 addresses but did not recognize IPv4-compatible IPv6 addresses with IPAddr#ipv4_compat?. An attacker could supply an address in the omitted range to bypass the ALLOWED_PRIVATE_ADDRESSES protection and make Mastodon send HTTP requests to loopback interfaces, potentially accessing private resources and services. Exploitation requires a system that supports the obsolete IPv4-compatible IPv6 mechanism. This issue is fixed in versions 4.4.21, 4.5.14, 4.6.4, and 4.7.0-beta.1.

## Affected Products

- mastodon — mastodon (< 4.4.21)
- mastodon — mastodon (>= 4.5.0-beta.1, < 4.5.14)
- mastodon — mastodon (>= 4.6.0-beta.1, < 4.6.4)

## References

- [CNA](https://github.com/mastodon/mastodon/security/advisories/GHSA-vwhj-3g83-v276)
- [CNA](https://github.com/mastodon/mastodon/commit/18c61f286f1f5718a8f517940ba384866ffa3892)
- [CNA](https://github.com/mastodon/mastodon/commit/467c933459c7d0e5513475b9e4888afaedfb1074)
- [CNA](https://github.com/mastodon/mastodon/commit/930aa9fee26bf9eaefe27826fa1061288d83373b)
- [CNA](https://github.com/mastodon/mastodon/commit/da47a1bd3cd07935d7ca55a1f4f1a76f7f167e0d)
- [CNA](https://github.com/mastodon/mastodon/releases/tag/v4.4.21)
- [CNA](https://github.com/mastodon/mastodon/releases/tag/v4.5.14)
- [CNA](https://github.com/mastodon/mastodon/releases/tag/v4.6.4)
- [CNA](https://github.com/mastodon/mastodon/releases/tag/v4.7.0-beta.1)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.36%
- **EPSS Percentile:** 29.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._